EP1.077.312 discloses an apparatus with which it is possible to keep two steam flows originating from two separate combustion processes completely separated until the steam is delivered to a steam turbine. Two sets of heat generation means are fluidly connected to a heat exchanger. Superheating of a steam flow from a first combustion process is being performed externally of the two combustion processes by the heat exchanger.
A problem to this apparatus is that it requires a large steam generation system. The steam generation system has a lot of steam generating means which makes it relatively expensive to build the steam generation system. It is desired to obtain a steam generation system having an improved configuration in that the amount of steam generating means are reduced. A further problem is that the installation is not arranged to be used with a solar energy steam generator.
DE 10144841 discloses a power plant which includes a gas turbine and a steam turbine. The power plant has a steam generator for generating steam which is guided to the steam turbine. The steam generator is provided with a first and second gas conduit which are arranged in parallel. Exhaust gasses from the gas turbine are conducted to the steam generator and distributed over the first and second gas conduit by a gas divider. Each gas conduit of the steam generator is provided with a series of heat exchangers. The first gas conduit comprises a conventional arrangement of heat exchangers including an economiser, evaporizer and superheater to produce a main steam flow. The second gas conduit comprises an economiser, a solar field as an evaporator and a superheater. The solar field is arranged in series with the economiser and the superheater within the second gas conduit.
In operation, the solar field may contribute to the generation of steam. Typically, the evaporation of steam originating from the solar field fluctuates which is caused by changing weather circumstances and day and night differences. By controlling the gas divider to control the amount of gas through the first and second conduit and by controlling a fed water flow which is supplied to the heat exchangers in respectively the first and second gas conduit, it is possible to use available steam generating capacity of the solar field. It is possible to use the steam generating capacity of the solar field to generate steam at a substantively constant temperature to add a generated solar steam flow to the main steam flow originating from the first gas conduit.
The arrangement is controllable to supply steam to the steam turbine at an optimum operating temperature of 500° C.±10K. The temperature is kept substantively constant. The steam turbine converts thermal energy into electricity and has an optimum capacity which depends from the temperature of the steam, but also from the steam mass flow. A problem to the disclosed power plant is that the steam generator generates a variable steam mass flow. The gas turbine is held constant at an optimum capacity to convert thermal energy into electricity. Herewith, the gas turbine generates a constant gas flow of exhaust gasses which are distributed and guided through the first and second gas conduits of the steam generator. When hardly no steam is generated at the solar field the mass flow of generated steam is reduced to the mass flow of the main steam flow generated in the first gas conduit. Due to the fluctuating mass flow, the steam turbine cannot always be fed with at an optimum mass flow. Thus, the steam turbine cannot operate at an optimum capacity. This reduces efficiency and implies for example that invested capital to build the power plant has to be re-earned over a longer term.
Additionally, the disclosed power plant is disadvantageous in that it is a relatively expensive plant to build and service. In fact, the power plant includes two complete steam generators. Furthermore, the power plant includes critical components. A problem to the power plant of DE 10144841 is that it includes a gas divider which is susceptible to damage or provides an unacceptable leakage of gasses. No prior art gas dividers are available which eliminates these problems. A first type of prior art gas dividers is referred as ‘Rauchklappe’ and includes a large guiding plate. The guiding plate may be positioned into two extreme positions to guide exhaust gasses to a first or second gas conduit. The large guiding plate is not suitable to be accurately positioned in an intermediate position. The large guiding plate would be impaired by vibrations which will damage the gas divider and which will substantively reduce the lifetime.
Problems of leakages will occur if a second type, including so called Louvre elements, of prior art gas dividers is used. The second type of gas dividers are provided with a series of elongated guiding plates which are arranged in parallel. Throughflows are provided in between the guiding plates which can be closed by rotating the guiding plates about their longitudinal axis. A problem to the second type of gas dividers is that these type of gas dividers is not suitable to resist a violent hot flow of exhaust gasses originating from a gas turbine. The elongated guiding plates will deform which will disable a necessary closure. Leakages will occur, which will impair the performances of the gas divider.
DE4300192 discloses an installation for the production of steam out of two combustion processes including an industrial combustion process providing a fluctuating heat as a first process. The installation comprises a gas turbine as a second stable combustion process. A problem to the installation is that the installation requires additional devices like high and low pressure boilers which makes the installation relative expensive and too complex. A further problem is that the installation is not arranged to be used with a solar energy steam generator. U.S. Pat. No. 6,279,312 discloses a steam generation system having a solar steam generator and a waste heat boiler. The solar steam generator comprises a solar field and comprises solar units having mirrors which are arranged to catch solar radiation and concentrate the radiation into a tube system which functions as a heat exchanger. Supplied water to the solar field is evaporated into steam and superheated and then used for steam injection purposes. Typically the steam generating production of the solar fields is fluctuating as a result of changes in weather and of course day and night differences. The complex character of fluctuating irradiated heat and the strong variety in temperature ask for an extra ordinary and flexible technology.
To compensate for the fluctuating steam generating production of the solar fields, the known steam generation system is provided with the conventional waste heat boiler. The conventional waste heat boiler with a heat exchanger and a steam drum is used as an auxiliary steam generator. The conventional boiler comprises three distinguishable in serial arranged heat exchange units. In a first stage water is supplied to the first heat exchange unit known as an economiser, wherein the supplied water is heated from a supply temperature of about 50° C. to an economic process temperature of just under saturation temperature. After the economiser, the water is supplied to an evaporator as the second heat exchange unit. In the evaporator water is evaporated into steam. Finally in a last stage of steam generation the steam from the evaporator is supplied to a super heater for superheating the steam. The three heat exchange units are all positioned within a common gas conduit of the boiler. The gas conduit is arranged to guide a flow of heating gasses which originate from a gas turbine as a main heat source. The three heat exchange units are all heated by the passing heating gas. A back-up firing equipment is provided including a burner which is controlled in such a way that the sum of the steam mass flows measured for the process steam and the injection steam corresponds to the specified overall flow.
In the known steam generation system, the solar field is connected in parallel with the evaporator of the boiler. The evaporator of the boiler serves as a back-up evaporator. Since the evaporator of the boiler is positioned in parallel with the solar field, it is possible to compensate for fluctuations in steam generation production of the solar field. Heating up the evaporator by the controlled burner increases the steam generating production of the back-up evaporator in the waste heat boiler to compensate for a reduction of the steam generating production of the solar field, for example during night or cloudy weather. As a result a steam generation system is provided which may provide at an outlet conduit to the steam turbine a constant steam flow.
A problem to known steam generation systems is that the reduction of steam generating production of the back-up evaporator is limited. The heating of the back-up evaporator is increased or reduced by the controlled burner to compensate for fluctuations in the steam generating production of the solar field. In the conventional boiler, the back-up evaporator is positioned downstream with respect to the flow of heating gasses flowing from the superheater within the gas conduit. The heating gasses from the gas turbine and the controlled burner together heat up the evaporator which results in the generation of steam. During operation, the heating gasses from the gas turbine are always present. The supply of water to the evaporator may be minimized to reduce the generation of steam, but there must always be a minimal flow of water through the evaporator to prevent overheating of evaporator components, like conduits and manifolds. Overheating of the conduits could lead to serious damage and stagnation of the steam generation process. Therefore in known steam generation systems, it is always ascertained that the evaporator within the boiler generates a minimum amount of steam in spite of the fact that the solar field generates already a sufficient amount of steam. As a result, it is impossible to accurately tailor the conventional boiler to the fluctuating steam generation production of the solar field.